Optical system for photographic film televising apparatus

ABSTRACT

An optical system for single-tube a photographic film televising apparatus in which Fourier transformation and spatial filter techniques are employed in the optical system for reproducing a monochrome photographic film having encoded color information to improve the S/N ratio and remove beat resulting from the construction of an encoder, so as to produce a high-grade reproduced television picture.

United States Patent 1 3,763,312 Yoneyama Oct. 2, 1973 1 OPTICAL SYSTEMFOR PHOTOGRAPHIC FILM TELEVISING APPARATUS inventor: M asahide Yoneyama,Kawasalii-shi,

Japan "Assignee: Nippon Coliiinliiaiiatiiish iliiliaisha,

Minato-ku, Tokyo, Japan Filed: Dec. 8, 1971 Appl No.: 205,808

Foreign Application Priority Data Dec. 12, 1970 Japan 45/110907 Dec. 19,1970 Japan 45/114885 Dec. 21, 1970 Japan 45/115481 US. Cl. l78/5.4 ST,l78/5.2 D Int. Cl. H04n 9/06 Field of Search 178/5.2 R, 5.4 R,

[56] References Cited UNITED STATES PATENTS 3,664,248 5/1972 Mueller178/5.2 R

Primary Examiner-Richard Murray AttorneyGeorge B. Oujevolk [57] ABSTRACTAn optical system for single-tube a photographic film televisingapparatus in which Fourier transformation and spatial filter techniquesare employed in the optical system for reproducing a monochromephotographic film having encoded color information to improve the S/Nratio and remove beat resulting from the construction of an encoder, soas to produce a high-grade reproduced television picture.

9 Claims, 12 Drawing Figures PAIENTED 0U 21973 :amwa

l 6. I l l F9. 20 w A I m I l l I MASAHIDE YONEYAMA ZNVENTOR BY GEORGEE. OUJEVOLK ATTORNEY Pmmmw P 3.763.312

sum ear 4 Ii g- 3 Iii g- 4 L11 4 /1 M 23 3 a? 5 5 fifWIAL FREQUENCY5FATIAL FREQUENCY lii. g- 5 br r fr) [Z 5'] FREQUENCY MASAHIDE YONEYAMAINVENTOR BY GEORGE B. OUJEVOLK ATTORNEY PAIENTED 21975 3. 763 3 1 2 sumanr 4 NASAHIDE YONEYAMA INVENTOR BY GEGRGE B OUJEVOLK ATTORNEYPATENTEDUBI 2 I975 SlEETMlF4 MASAHIDE YONEYAMA INVENTOR I-TLB BY GEORGEB OUJEVOLK ATTORNEY OPTICAL SYSTEM FOR PHOTOGRAPHIC FILM TELEVISINGAPPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to an optical system for a photographic filmtelevising apparatus, and more particularly to an optical system forreproducing an encoded monochrome film containing encoded colorinformation.

2. Description of the Prior Art In a reproducing optical system for aconvention television film camera, an image of an object recorded on aphotographic film is projected onto a target of an image pickup tube ofthe television camera by means of a film projector having a white lightsource and converted into a television signal to be reproduced. In thiscase, the image of the object is picked up and reproduced throughvarious transmission systems, and hence it is subjected to undesirableinfluences of the transmission characteristics of the transmissionsystems, which leads to deterioration of the picture quality. A firstproblem is lowering of the spatial frequency response of the imagepickup tube in a high-frequency range. A second problem is lowering ofthe spatial frequency response of the film which is caused by theoptical transfer function of the film itself, the special frequencyresponse of the film being lowered in a high frequency range. A thirdproblem arises from a rear protective glass interposed between the filmand an optical modulation grating especially in the case of themonochrome color film. The rear protective glass causes defocusing ofthe image of the modulation grating on the film, so that it is necessaryto make the glass thin but this is limited technically.

In order to compensate for the lowering of the response in thehigh-frequency range, it is the practice in the prior art that, afterthe optical image is converted by an image pickup tube into a televisionsignal, the high-frequency component of the signal is emphasized.However, this also emphasizes noise generated by a preamplifier of thecamera and discrete noise of high spatial frequency range due to theshape of silver particles of the photographic film, causing a decreasein the S/N ratio.

In a system (hereinafter referred to as a monocolor system) of the typethat color information of an object to be televised is recorded on amonochrome film together with luminance information of the object and acolor signal is reproduced by a television camera from the film, thepitch of strip filter elements for encoding the color infonnation isselected such that red and blue color carrier frequencies, which aregenerated by scanning of an optical image of a filter projected on thetarget of the television camera in accordance with the standardtelevision system, may be, for example, 3.9MHz and 5.1MHz respectively.Usually, two striped filters (red and blue striped filters) are placedone on the other, so that when the optical image projected on the targetis scanned a point where red and blue color inhibiting portions agreewith each other repeatedly appears on the same scanning line. Therepetitive frequency (hereinafter referred to as a beat frequency) ofthe points is the difference between the aforementioned red and bluecolor carrier frequencies, that is, for example, l.2MHz.

Since the aforesaid beat frequency component lies in the frequency bandof a luminance signal, it appears as a stripe pattern in the reproducedpicture to degrade the picture remarkedly. In the case of employing aband-rejection filter for electrically removing the beat component,necessary luminance signal component is lost to deteriorate the picturequality greatly.

SUMMARY OF THE INVENTION One object of this invention is to provide anoptical system for photographic film apparatus in which thecharacteristic of an optical image transmission system is corrected byFourier transformation and spatial filtering treatment with coherentlight without deteriorating the S/N ratio.

Another object of this invention is to provide an optical system forphotographic film television apparatus in which the spatial frequencyresponse characteristics of an image pickup tube and/or a film arecorrected by Fourier transformation and spatial filtering treatment withcoherent light without deteriorating the S/N ratio thereby to obtain ahigh-grade reproduced picture.

Still another object of this invention is to provide an optical systemfor photographic film television apparatus in which a beat signalcomponent is removed by Fourier transformation and spatial filteringtreatment with coherent light without deterioration of the picturequality thereby to obtain a high-grade reproduced picture.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1A and 1B are schematic diagramsof a frequency separation type color signal generating device, forexplaining this invention;

FIGS. 2A, 2B and 2C are diagrammatic showings of striped filtersemployed in the device of FIGS. 1A and 18;

FIG. 3 is a graph showing one example of the spatial frequency responseof an optical transmission system such as an image pickup tube, a filmor the like;

FIG. 4 is a graph showing one example of a correcting function forcorrecting the spatial frequency response of the optical transmissionsystem;

FIG. 5 is a graph showing bandpass characteristics, for explaining thisinvention;

FIG. 6 is a diagram illustrating one example of a reproducing opticalsystem of this invention;

FIG. 7 is a diagram showing one example of the construction of a spatialfilter of this invention; and

FIGS. 8 and 9 diagrams illustrating other examples of the spatial filterusuable in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding ofthis invention, a description will be given first of a single-tube colorcamera of the frequency separation type.

'In FIGS. 1A and 18 there is shown the construction of a known colorcamera of the monocolor system proage. The two striped filters 4 and 5make up an optical modulation grating and the monochrome photographicfilm 6 is disposed close to the back of the filter 5. While, in thereproducing system the film 6 with the information recordcd thereon asabove described is projected onto the target of an image pickup tube 9of a television camera by means of a film projector 8 having a whitelight source 7, by which the information is converted into an electricsignal and then color signals contained therein are separated bybandpass filters from each other for reproducing.

The constructons of the striped filters 4 and 5 are shown in detail inFIGS. 2A and 28 respectively. The filter 4 consists of strip filterelements 41 inhibiting the passage therethrough of red colored light andstrip filter elements 42 permitting the passage therethrough of allcolored light. The strip filter elements 41 and 42 are alternatelyarranged at a repetitive pitch Pr and inclined at an angle Or to ahorizontal axis H. Similarly, the filter 5 consists of strip filterelements 51 and 52 alternately arranged at a repetitive pitch Pb acrossa horizontal axis H at an angle 6b thereto. The strip filter elements 51inhibit the passage therethrough of blue colored light and the stripfilter elements 52 permit the passage therethrough all colored light.The pitches Pr and Pb of the strip filter elements of the stripedfilters are selected such that red and blue color carrier frequencies,which are generated by scanning the optical image projected onto thetarget of a television camera in accordance with the standard televisionsystem, may be, for example, 3.9MI-Iz and 5.1MI-Iz. The front and backof the striped filters 4 and 5 are protected with transparent glassplates 4 and 5 Namely, the striped filter 4 is formed by arranging thestrip filter elements 41 on the back of the transparent glass plate 4 atthe pitch Pr and the striped filter 5 is likewise formed by arrangingthe strip filter elements 51 on the front of the transparent glass plate5 at the pitch Pb. In practice, the transparent glass plates 4 and 5perform the function of the aforemantioned filter elements 42 and 52respectively.

As is well-known, the Fourier transformation spectrum of a diffractiongrating is a line of dots spreading out about a ray or light axis on aline perpendicular to the lines of the grating. When the grating isturned in a plane perpendicular to the ray axis, the line of dots turnstogether with the grating while being held perpendicular to the line ofgrating. Further, it is also wellknown that when the grating and theobject are superimposed on each other in the forward focal plane of atransformation lens, a diffraction image of the grating including thespectrum of the object appears in the transformation plane and thespectrum of the object is seen in each light portion of the diffractionimage (diffraction order) of the grating.

In the monocolor system, the red and blue color components of therecorded image are an optical image due to superimposition of thestriped filters 4 and 5 making up the modulation grating. Accordingly,the spatial frequency spectrum distributions of the red and blue colorcomponents are concentrated in the vicinity of areas at which knownspatial frequency spectrum distribution of the modulation grating appearbut the distribution density of the red and blue color components is lowin the other areas. On the other hand, the spatial frequency spectrum ofthe discrete noise of the film is distributed substantially uniformly inthe spatial frequency transmission band of a signal, so that all ofnoise spectrums in the transmission band exert an influence on thereproduced picture.

While, the green color component of the recorded image has nointerrelation to the modulation grating and its spatial frequencyspectrum is mainly distributed in a relatively low frequency rangewithin the spatial frequency band, so that the green color component isnot greatly affected by the discrete noise of the film.

FIG. 6 shows one example of the construction of the reproducing opticalsystem of this invention. The light source 10 is a source of coherentlight such as Hie-Ne gas laser or the like and rays of light emittedfrom the light source 10 are rendered by a collimator lens 11 into abeam of parallel rays. Where a recorded encoded monochrome film 6 isplaced in the forward focal plane of a second lens 12 having a focaldistance f,, a spatial frequency spectrum of amplitude distribution ofthe film 6 appears in the backward focal plane (Fourier transformationplane) of the lens 12. A spatial frequency filter 13 is disposed in theFourier transformation plane of the lens 12. When the spectrum image inthe Fourier transformation plane of the lens 12 is again subjected tothe Fraunhofers diffraction in the backward focal plane (herein referredto as a reproducing plane) of a third lens 14 of a focal length fdioposed in such a manner that the Fourier transformation plane of thelens 12 and the forward focal plane may coincide with each other, anoptical image of the film 6 having passed through the spatial filter 13is obtained in the reproducing plane. The optical image of the film 6appearing in the reproducing plane is converted into an electric signalby an image pickup tube 15 which is disposed with its image picking upplane coinciding with the reproducing plane. It is needless to say thatthe above optical means are all aligned on the same ray or light axis L.

In order that the spatial filter 13 disposed in the Fouriertransformation plane of the lens 12 may compensate for lowering of thespatial frequency responses of the image pickup 15, and/or the film 6and the lowering of the spatial frequency response caused by the glassplate 5 it is sufficient only to provide an amplitude transmissionfactor distribution which is opposite to their spatial frequencyresponse characteristics.

Generally, the spatial frequency response of the image pickup tube is ofsuch a characteristic as shown in FIG. 3 and the response at a spatialfrequency S reduces down to ll/A of that in the lower frequency range.The spatial frequency response of the film and the glass plates is of asimilar characteristic. Put the spatial frequency response of the imagepickup tube H,(u, v), put that of the film H (u,v) and put that due tothe thickness of the glass plate H (u, v), a correcting function T (u,v) is as follows:

T w) (N 2 W' a Accordingly, the general characteristic of the correctingfunction T (u,v) is such as shown in FIG. 4, in which the response atthe frequency S is A times that in the lower frequency range.

Since co-ordinates in the Fourier transformation plane are proportionalto the spatial frequency, a locus of a point of equal effective spatialfrequency becomes circular about the ray axis. Put its radius r, thefollowing relation holds.

r=fls.....

wherefis the focal length of the lens, I the wavelength of light and sthe effective spatial frequency.

A description will be given in connection with one method for obtaininga spatial filter of such an amplitude transmission factor distributionas above described.

From a grey but transparent material of a transmission factor T per unitthickness such as used for making a neutral density filter forphotographic camera, a columnar transparent member is formed which has arelative thickness of l at its ray axis and gradually increases itsthickness from the ray axis towards its peripheral edge in such a manneras to satisfy the condition that the relative thickness d on thecircumference of a radius r about the ray axis defined by theaforementioned equation (2) corresponding to the spatial frequency S isl/A 7, that is,

dlogT=l0gA.....

This transparent member is irradiated by parallel rays of light from thedirection of its ray axis and the monochrome photographic film isexposed rays of light having passed through the transparent member. Thecontrast of the negative film thus obtained is 1 in the vicinity of theray axis and l/A on the circumference of the circle with the radius r.Namely, the negative film constitutes a spatial filter having apredetermined amplitude transmission factor distribution.

FIG. 7 shows one example of such a spatial filter, which is disposedwith its x and y planes coinciding with the Fourier transformation planeof the first optical device and its x axis with its ray axis.

In order to decrease the influence of the discrete noise of thephotographic film, use is made of a spatial filter having such anamplitude transmission factor distribution which selectively permits thepassage of areas of an image having dense spectrum distribution andinhibits the passage of areas having low spectrum distribution. The useof such a spatial filter enhances the SN ratio of the reproduced picturewithout decreasing the amount of information of the picture beingrecorded.

FIG. 8 illustrates one example of the construction of the spatial filterwhich is employed for decreasing the discrete noise of the film. In thefigure, the spatial filter 13 consists of a circular region 130permitting the passage therethrough of the green color component of theimage to be recorded, circular regions 132 and 133 permitting thepassage therethrough of the red color component, circular regions 135and 136 permitting the passage therethrough of the blue color componentand light inhibiting region 13A. The center of the region 130 lies onthe ray axis L and those of the regions 132, 133, 135 and 136 on astraight line 131 passing through the ray axis L, perpendicular to thered color inhibiting filter elements 41 and crossing a vertical axis atan angle Or and on a straight line 134 passing through the ray axis L,perpendicular to the blue color inhibiting filter elements 51 andcrossing the vertical axis at an angle 0b respectively. 0r and 0bare'the angles beequations.

where f is the focal distance of the lens 12, l the wavelength of thecoherent light emitted from the light source 10, and S, and S, theeffective spatial frequencies of the striped filters 4 and 5respectively.

The radiuses Rg, Rr and Rh of the respective circular transmissionregions are related to the transmission bands of the corresponding colortelevision signals and given by the following equations.

1- fl r o fl b where k is a coefficient of transformation from spatialfrequency to time frequency, and Hg, Br and Rh transmission band widthsof the red, green and blue color component television signals, the bandwidths being selected, for example, as follows Bg 3Ml-Iz Br Bb 0.4MHZ.

With the use of such a spatial filter, it is not necessary to emphasizeand amplify the high-frequency component of the signal output derivedfrom the image pickup tube, so that the noise generated by thepreamplifier of the camera is not ever emphasized and the discrete noisecomponent of the film can be effectively removed to improve the SNratio, thus providing a high-grade reproduced picture.

Since the beat component is produced by mutual modulation of the imagesof both the striped filters, its Fourier spectrum appears at theintersection of two straight linespassing through the points at whichFourier spectrum of modulation grating appears and perpendicular to thegrating. However, the spectrum appearing at the intersection of thestraight line passing through the point of the primary diffraction comesinto problem. Its horizontal co-ordinate corresponds to the differencebetween the red and blue color carrier frequencies, for example,1.2MI-Iz. In order to remove this optically, it is sufficient only toprevent that the optical image appearing at the aforementioned positionon the Fourier transformation plane is transmitted to the reproducingplane.

FIG. 9 shows one example of a spatial filter employed for this purpose.

In FIG. 9, points 132a and 133a on the straight line 131 arerepresentative of the primary diffraction of the red color inhibitingstriped filter 4 and the distances from the ray axis L to them aredetermined by the equation (2) dependent upon the spatial frequency ofthe red color inhibiting filter 4. While, points 135a and 136a on thestraight line 134 are representative of the primary diffraction of theblue color inhibiting striped filter 5 and the distances from the rayaxis L to them are determined by the equation (2) in accordance with thespatial frequency of the blue color inhibiting striped filter 5. Astraight line 137 passes through the point 133a and is parallel to thestraight line 134 and a straight line 138 passes through the point 135aand is parallel to the straight line 131. The center of a small circle139a is the intersection of the two straight lines 137 and 138 and itshorizontal co-ordinate corresponds to the difference between the red andblue color carrier frequencies as previously described. A small circle13% is symmetrical with that 139a relative to the ray axis L. Thecircles 139a and l39b in the spatial filter 13 are light inhibitingregions and the remaining regions are light transparent regions.

With the provision of the spatial filter of the above construction inthe Fourier transformation plane of the reproducing optical system, onlyharmful beat components can be removed without affecting any influenceon required luminance signal component, thereby to provide for enhancedpicture quality.

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts of thisinvention.

1 claim as my invention:

1. In a television image transmission system including a televisioncamera having an image pickup tube with a predetermined spatialfrequency response and wherein the image of an object is recorded on amonochromic photographic film with a single color light emitted from apoint light source, said monochromic photographic film having recordedthereon luminance information and a plurality of color information ofthe object image, said image of the object having been recorded on saidfilm after passing through an optical modulation grating consisting of aplurality of strip filter elements of different frequencycharacteristics, in combination:

a. a first optical means defining a Fourier transformation plane forFourier transformation of said image;

b. a spatial filter disposed on the Fourier transformation plane of saidfirst optical means, said spatial filter having an amplitudetransmission factor distribution which is the reciprocal of the spatialfrequency response of said image pickup tube; and,

c. a second optical means defining a plane for inverse Fouriertransformation of the spatial frequency spectrum obtained from the firstoptical means,

said television camera being disposed opposite said second optical meansfor picking up an optical image formed on the Fourier transformationplane of said second optical means.

2. An optical system for photographic film televising apparatus asclaimed in claim 1, wherein the spatial filter has an amplitudetransmission factor distribution which is a reciprocal of a specialfrequency responses of the photographic film.

3. An optical system for photographic film televising apparatus asclaimed in claim 2, in which the amplitude transmission factordistribution is determined by the pitches of the strip filter elementsof the optical modulation grating and the transmission characteristic ofa television signal corresponding to the color characteristics of thestrip filter elements.

4. An optical system for photographic film television apparatus asclaimed in claim 3 in which the spatial filter has a first circularregion permitting passage therethrough of a green color component fromthe image, a second circular region permitting passage therethrough of ared color component, a third circular region permitting passagetherethrough of a blue color component and a light inhibiting region.

5. An optical system for photographic film television apparatus asclaimed in claim 4 in which the first region is disposed on the ray axisand said second and third regions are disposed on different distancesfrom the ray axis.

6. An optical system for photographic film televising apparatus asclaimed in claim 2, in which the amplitude transmission factordistribution cuts off mutual modulation component determined by thepitch of the strip filter elements of the optical modulation grating.

7. An optical system for photographic film television apparatus asclaimed in claim 6 in which the spatial filter includes two regions, oneof which passes therethrough all color lights but the other of whichinhbiits passage of all color lights therethrough.

8. An optical system for photographic film television apparatus asclaimed in claim 7 in which the region inhibiting passage therethroughof all color lights consists of two circles disposed symmetrical withrespect to the ray axis. 7

9. An optical system for photographic film television apparatus asclaimed in claim 8 in which one of said two circles is disposed with itscenter on the intersection of two lines, one of which passes through apoint tion of a blue color inhibiting striped filter element.

1. In a television image transmission system including a televisioncamera having an image pickup tube with a predetermined spatialfrequency response and wherein the image of an object is recorded on amonochromic photographic film with a single color light emitted from apoint light source, said monochromic photographic film having recordedthereon luminance information and a plurality of color information ofthe object image, said image of the object having been recorded on saidfilm after passing through an optical modulation grating consisting of aplurality of strip filter elements of different frequencycharacteristics, in combination: a. a first optical means defining aFourier transformation plane for Fourier transformation of said image;b. a spatial filter disposed on the Fourier transformation plane of saidfirst optical means, said spatial filter having an amplitudetransmission factor distribution which is the reciprocal of the spatialfrequency response of said image pickup tube; and, c. a second opticalmeans defining a plane for inverse Fourier transformation of the spatialfrequency spectrum obtained from the first optical means, saidtelevision camera being disposed opposite said second optical means forpicking up an optical image formed on the Fourier transformation planeof said second optical means.
 2. An optical system for pHotographic filmtelevising apparatus as claimed in claim 1, wherein the spatial filterhas an amplitude transmission factor distribution which is a reciprocalof a special frequency responses of the photographic film.
 3. An opticalsystem for photographic film televising apparatus as claimed in claim 2,in which the amplitude transmission factor distribution is determined bythe pitches of the strip filter elements of the optical modulationgrating and the transmission characteristic of a television signalcorresponding to the color characteristics of the strip filter elements.4. An optical system for photographic film television apparatus asclaimed in claim 3 in which the spatial filter has a first circularregion permitting passage therethrough of a green color component fromthe image, a second circular region permitting passage therethrough of ared color component, a third circular region permitting passagetherethrough of a blue color component and a light inhibiting region. 5.An optical system for photographic film television apparatus as claimedin claim 4 in which the first region is disposed on the ray axis andsaid second and third regions are disposed on different distances fromthe ray axis.
 6. An optical system for photographic film televisingapparatus as claimed in claim 2, in which the amplitude transmissionfactor distribution cuts off mutual modulation component determined bythe pitch of the strip filter elements of the optical modulationgrating.
 7. An optical system for photographic film television apparatusas claimed in claim 6 in which the spatial filter includes two regions,one of which passes therethrough all color lights but the other of whichinhbiits passage of all color lights therethrough.
 8. An optical systemfor photographic film television apparatus as claimed in claim 7 inwhich the region inhibiting passage therethrough of all color lightsconsists of two circles disposed symmetrical with respect to the rayaxis.
 9. An optical system for photographic film television apparatus asclaimed in claim 8 in which one of said two circles is disposed with itscenter on the intersection of two lines, one of which passes through apoint representing the primary diffraction of a red color inhibitingstriped filter element and the other of which passes through a pointrepresenting the primary diffraction of a blue color inhibiting stripedfilter element.